When I taught Introductory Psychology, I came across a study in which researchers put people in a room with food and watched them. They were looking for cycles in eating and drinking. They noticed that their subjects spent a lot of time touching the face near their mouth — what they called “the snout area”. After I read that, I noticed the same thing countless times. Right now I am at an airport waiting for a flight. Looking around, I see three of about 50 people touching their mouth or nearby.
Why do we do this? I propose an evolutionary explanation: To expose our immune system to all the germs near us in small amounts. Mouth-touching is part of a larger sampling process: 1. We touch many things constantly. In particular, we shake hands, hug, and otherwise touch people near us. Germs that have managed to live in or on other people are the most dangerous. 2. We lick our lips often, moving germs on our lips inside our mouths. 3. When you eat, food transfers bacteria from the inside of your mouth to your tonsils, which circle your throat. Tonsils are full of lymphocytes, the immune-system cells that detect germs. Once we have developed antibodies to a microbe, of course, we are much less vulnerable to it. The whole sampling process is a kind of self-vaccination.
We need conventional vaccination when self-vaccination fails. Polio vaccination was the first big vaccination program, and it worked: polio was nearly wiped out. Before around 1900, polio was not a big problem. It became a big problem at roughly the same time that public health measures and the replacement of horses by cars caused cities to become much cleaner places. Others have theorized that this is why polio became a big problem. As recently as 1951, thousands of children died from polio.
This is related to but different than my ideas about our need for fermented food. (I believe we need to eat plenty of fermented food, day after day, to be healthy.) When we eat fermented food, we ingest large amounts of bacteria that are familiar and safe. The amount is large because the food has been fermented. The bacteria are familiar because we eat the same food repeatedly. They are safe because the insides of our bodies are dramatically different than what we eat (e.g., different temperature). The sampling system I am proposing here exposes us to small amounts of unfamiliar dangerous bacteria. However, this sampling system and the factors that push us to eat fermented food (our liking for complex, sour, and umami flavors) both act to produce the best environment for our immune system. Fermented food resembles exercise and practice; the mouth-touching system resembles information.
A similar sampling system is our love of gossip. We love to hear it, we love to spread it. Gossip spreads information about the dangers around us. Again, forewarned is forearmed.
I am in Tokyo (for a few more minutes), an admirably clean city. Public rest rooms, for example, are convenient, clean, and free. (Unlike New York, Los Angeles, San Francisco, Beijing . . . ) The practical point of this idea isn’t that there is something wrong with public health measures, it is that they can go too far.